Electric vehicles with large storage batteries represent an underutilized resource that can serve to stabilize the electric utility grid and reduce the requirement for additional investment in distribution and transmission equipment, if they can be remotely directed to take or provide AC power. The communication technology for the remote control exists, together with an existing market for ancillary services to the grid. Solar inverters can convert DC power from the battery to AC power for the grid.
This bidirectional flow of power can provide valuable services to the utility grid. An example of the latter is frequency regulation in which battery storage can take excess power or provide needed power instantly on request from the Independent System Organization or Regional Transmission Organization (ISO/RTO) responsible for grid stability. The ISO/RTOs pay for this ancillary service in a daily auction market. Another service is demand response in which the battery can stop charging at periods of peak demand when the power is needed elsewhere on the grid. This sery ice is also recompensed by the RTO/ISO.
For commercial and industrial vehicle owners, the vehicle battery can provide power to offset peak demand during the daytime and thus reduce the monthly demand charge imposed by the local distribution company. There is an opportunity for energy arbitrage in which the vehicle is charged at night when prices are low and partially discharged during the day if the value of the power is greater than its value in propelling the vehicle.
This invention utilizes the photovoltaic inverter of an existing solar photovoltaic system, and the on-board charger provided with the vehicle to provide a minimum-cost, bidirectional Electric Vehicle PhotoVoltaic (EVPV) interface. This interface can be programmed to maintain the vehicle in a suitable state of charge to provide the driving range needed by the owner using power from the grid at the optimum time to minimize cost, and to provide ancillary services to the grid to generate revenue to offset the cost of the vehicle and its energy supply.
The availability of AC power flow from the battery also provides a back up power supply to the vehicle owner when there are grid outages to maintain essential services such as heating and water pumps. This capability is particularly valuable in conjunction with a solar photovoltaic array which can provide power to keep the battery and the vehicle charged during outages and which in turn can be kept operating by “islanding” from the grid rather than shutting down as required by IEEE standard 1547 to avoid putting power back on the grid during an outage.
For both ancillary service and owner service it is an advantage to have the battery connected at all times to maximize revenue and convenience. However, by the nature of a vehicle, the vehicle battery is going to be disconnected when the vehicle is in use. This may be for as little as an hour or two or as much as 8 or 10 hours per day depending on use of the vehicle. An auxiliary stationary battery may be provided to maintain continuity of service while the vehicle is in use.